1. Field of the Invention
This invention relates generally to injection molding. In particular, this invention relates to devices used for equalizing separation of mold members in so-called “stack mold” arrangements as mold assemblies are opened and closed.
2. Description of Related Art
It is known to arrange mold members in so-called “stack molds” to increase the number of articles that may be molded with a single cycle of operation of a molding machine. A “stack mold” is characterized as having two or more mold assemblies arranged so that intermediate mold members or mold assemblies are interposed between mold members mounted to, respectively, a stationary platen and a movable platen of a molding machine clamp unit. In certain of such known arrangements used in injection molding: a first mold assembly is arranged with a first mold member connected to a stationary platen (also referred to as a “fixed platen”); a second mold assembly is arranged with a third mold member connected to a movable platen; and a second mold member comprising the first mold assembly and a fourth mold member comprising the second mold assembly are supported so as to be interposed between and opposing, respectively, the first mold member and the third mold member and to be movable relative thereto. The interposed mating mold members are referred to herein collectively as “intermediate mold members” or “intermediate mating mold members”. A mold assembly is “closed” when the mating mold members are abutted; a mold assembly is “open” when the mating mold members are separated. Opening and closing of the mold assemblies is effected by moving the movable platen and the intermediate mold members to separate and abut, respectively, the first and second mating mold members and the third and fourth mating mold members. Motion of the movable platen is effected by at least one actuator comprising a clamp mechanism and motion of the movable platen is mechanically coupled to the intermediate mold members. It is known to provide rack and pinion mechanisms to couple movement of the movable platen to the intermediate mold members so that separation of mating mold members is kept equal as the mold assemblies are open and closed. Such rack and pinion mechanisms are known as “centering devices”.
It is known to dispose rack and pinion centering devices in stack mold arrangements so as to have a pinion mounted for movement with the intermediate mold members; to have an end of a first rack fixed relative to the mold member associated with the stationary platen; to have an end of a second rack fixed relative to the mold member associated with the movable platen and to have the otherwise free ends of the first and second racks engaging opposite sides of the pinion. Movement of the movable platen is translated to rotation of the pinion by the second rack and rotation of the pinion is translated to translation of the intermediate mold members by interaction of the pinion and the first rack. The translation of the intermediate mold members partially offsets translation of the first rack relative to the pinion so that separation between the intermediate mold members and, respectively, the fixed and movable mold members is equalized as the mold assemblies are opened and closed.
Mating mold members are designed to achieve a predetermined “mold height”, that is, overall thickness when opposed faces of mating mold members are abutted, (mold is “closed”). The overall thickness of the abutted mold members is predetermined. While it would be preferred to rely on the predetermined dimension of mold height to machine mold members for attachment of centering devices before installation of the mold members and centering device in a machine, actual mold height may differ from the design value. To accommodate such differences, it is known to perform attachment point machining on the racks and/or mold members with the mold assemblies in place in the machine clamp unit to achieve the required relative location of racks and mold members. Because such machining requires tools suitable to be supported to access locations of the installed mold members and racks, it is done manually. Such manual machining increases the time required to complete installation of a mold assembly in the clamp unit of a machine. Hence, there is a need to permit mounting of rack and pinion centering devices so as to accommodate differences in mold height from design values so as to eliminate the need for such manual machining.